High impact polystyrene



The present invention relates to molding compositions comprising polyvinyl aromatic compounds. ticularly, this invention relates to a high impact polystyrene molding composition.

It is known that polyvinyl aromatic compounds such as polystyrene have improved properties of toughness I when a small amount of rubbery polymer is incorporated therewith. It is also known that in order to mold thermoplastic compositions such as polystyrene it is necessary to employ agents to improve the moldability of the compositions. Thus, it is important to include a lubricant with the composition in order to give the desired properties of flow, preventsticking to the mold, and the like. However, the use of a lubricant, even in relatively small amounts has a marked effect on the strength properties of polyvinyl aromatic materials such as polystyrene.

It is a primary object of this invention to provide a lubricant for polyvinyl aromatic molding compositions which provides the desired flow properties. Another object of this invention is to provide a lubricant for polyvinyl aromatic compositions which provides the desired toughness and yet which is comparatively inexpensive.

These 'and other objects are accomplished by incorporatinga lubricant in polyvinyl aromatic molding compositions, which lubricant comprises from about 1.5 to

about 3.5 parts by weight of a parafiin wax and from 0.5 to about 2.5 parts by weight of a member of the group consisting of hydrocarbon oil and a highly naphthenic wax.

In its broad aspect, the present invention embraces molding compositions of vinyl aromatic resins which are solid polymers and copolymers of vinyl aromatic compounds having the'vinyl group attached to a carbon atom of the aromatic nucleus substituted with one or more groups such as methyl, ethyl and chloro groups. However the preferred polyvinyl aromatic resins utilize styrene as the vinyl aromatic constituent. In addition to the vinyl aromatic constituent, the molding compositions of the present invention may also contain a rubbery polymer in order to improve the properties of toughness. Such rubbery polymers contain a major portion of the polymerization product of conjugated diolefins and a minor proportion of styrene. Examples of such rubber polymers include polybutadiene, polyisoprene, copolymers of butadiene and styrene and copolymers of butadiene and acrylonitrile. The preferred polymers suitable for this invention consist essentially of styrene and butadiene components.

The relative proportions of polyvinyl aromatic material and rubbery polymer should be within the range of from about 85 to 98 parts by Weight of polyvinyl aromatic materials and from about 2 to about 15 parts by weight of rubbery polymer. 1

More par- United States Patent The lubricant used in thexpresent invention consists,

I essentially of about 1.5 to about 3.5 parts by weight of a paraffin wax and from 0.5 to about 2.5 parts by weight 'of a member of the class consisting of a hydrocarbon oil and a highly naphthenic wax. The amount of lubricant used will vary with the particular resin and the properties desired, but it will generally be within the range of from ddlllh Patented Apr. 6, 1965 ice about 1 to about 6 parts by weight of lubricant per 100 parts by weight of resin. The lubricant is preferably substantially free of olefinic and aromatic constituents. The blend of parafiin wax and hydrocarbon oil or highly naphthenic wax is required in the present invention in order to obtain the desired balance of properties. Thus, paraffin wax generally provides rather high impact strength but .it also generally gives insufiicient elongation and sometimes insuificient flow. The hydrocarbon oils and highly naphthenic waxes used in the present invention, on the other hand, provide the desired properties of elongation and flow, but do not provide a sufficiently high yield strength.

It has now been found that by utilizing the parafiin waxes of comparatively low molecular weights, as waxes go, it is possible to eliminate the problem of insufiicient flow, and by blending hydrocarbon oil with such a paraffin wax, it is possible to provide the desired elongation. Higher molecular Weight hydrocarbons seem to increase the flow temperature (Rossi-Peakes) and the hydrocarbons having more than 30 carbon atoms should be held to a minimum. Thus it is preferable to use hydrocarbons which are normal or substantially normal and for best results the hydrocarbon wax should have above about 60% normal parafiins. The term n-parafiin means a straight chain alkane with nobranching whatever.

The hydrocarbon oil may be any of those known in the trade as white mineral oils. Such mineral oils consist principally of saturated aliphatic hydrocarbons and those applicable to the present invention have a boiling point between about 400 and l,000 F. and preferably have a gravity of above 30 API at 60 F.

As mentioned above, such materials provide excellent elongation and fairly'good flow temperatures, but are unsatisfactory by themselves because they seriously reduce the yeld strength which is otherwise attainable. A typical example of a preferred mineral oil hereinafter referred to as Mineral Oil Ahas a gravity of 325 API, a pour point of 15, a viscosity (Universal Saybolt seconds at 100 F.) of 104 and an initial boiling point of 584 F. v

The parafiin Wax usedin the. preparation of the lubricant'of the present invention is obtained from the crude wax product which is obtained when lubricating oils having parafiin wax are dewaxed according to conventional refinery techniques. Examples of paraffin waxes which may be used in the present invention are illustrated as the procedures given below:

Paraflin wax A.A light lube oil fraction is obtained by avacuum distillation of that portion of a crude which remains after the light fractions have been removed, by atmospheric distillation. This light oil is treated to remove aromatics in a conventional phenol extractor, and

the rafiinate from the extractor is dewaxed in a dewaxing unit using methyl ethyl ketone as the solvent. In the dewaxing unit, the raffinate and solvent is filtered at a low temperature to remove the solidified crude wax from the liquid oil. The crude wax thus obtained is sent to a wax deoiling unit where the wax is melted again in the presence of solvent and cooled only to an amount suflicient that the-high melting wax components crystallize. The raw wax from the wax deoiling unit is usually sent to a finishing unit wherecertain impurities present in minute amounts are removed to provide a marketable finished wax.

The wax thus obtained from the light fractions will generally contain about normal paraffins depending on the type of crude oil which enteredthe refinery inthe first 1 phase. However, :analysisof, various light fractions of WestTexas-crudes show that for waxes thus obtained which have a melting point of from 121-1'25 'F., the usual range is from about 80 to about 97% normal alkanes, thebranched or isoalkanes are usually from about 2 to 20% and generally'from about 2 to by volume, andthe naphthenic or cycloalkanes will be less than 5% and usually less than 2%. 'Aromatic materials are present only in trace amounts, and olcfinic materials are not tound by analysis.

Paraffin wax B..After the light lubricating oil fraction is obtained as mentioned in the procedure above for p-arafiin wax A,,a medium lubricating oil is obtained by fur-. therdistillation at isubatmosplreric pressure to provide a medium lube oil. This oil is dewaxed and the wax treated I as mentioned :above to provide a finished wax from the medium distillatelubricating oil. This wax contains components having a somewhat higher molecular Weight than the waxobtained from the light fraction because of the higherboiling points involved, and generally will contain less normal alkanes .and, more branched and cyclic alkanes. A typical wax inaction thus obtained which has a melting point from about 138 to 140 F.,c0ntains from about 70' to 80% normal alkanes', from about 8 to isoalkanes and iirom about 6 toabout 15% cycloalk-anes.

Paraffinwax c.-s7 lparts of parafiinwax B @443 1 parts of parafiin wax A were blended together to forma v and highyield strengths but it is seen frorn'the table that 7 r r 4 speeds. Specimens' were compression-moldedand tested for the properties listed in Table I below.

'All of the give fairly good impact strength the high, molecular weight waxes appearitoprovide insufficient flow. .In addition; all .of :the. paraflin waxes shown above except that which contains a fairly good per-, centage of naphthenic composition:gave'insuflicient elongation. Thus'none of the paraifin waxes are. suitable by themselves eventhough they give excellent imp'actresistanceaand yield strength; 7

In accordance With-thepresent invention, a blend of the low molecular-weightparaflin'waxes with oils or soft waxes (highly naphthenic waxes), provides the desired elongation and yet retains a good, yieldstrength and high homogeneous mixture. The resulting wax has a melting point of about 132 to 134F.

The above waxes were used as lubricants in preparing a bulk interpolymer of styrene and a styrene-butadiene 1 copolymer inaccordance with the procedure which will be given hereinafter. In addition to these materials, waxes having considerably higher molecular weights were also tested. These molecular weight waxes may be labeled as paraiiin wax D'which has a melting point of 158-162 F. and contains a much higher percentage of isoalkane and naphthenes than-paraflin waxes A through C. In additionthe molecular weights were much higher,

' and theiaverage number of carbon atoms' was above.

and probably of the order of, say, 33.

obtained by urea extraction of thewaxy portion from still bottoms andtherefiore is substantially free of naphthenic constituents. It has a melting point of about 180 F. and has an :average number of carbon atoms of theorder: of,

' say, about-40 carbons.

Table I below gives the efifect of these lubricants and certain of the physical properties of the bulk polymer-containing 4 of wax per .100 parts of resin. consisted of a solution of 5% 8-1006 (a hot rubber containing 77% .butadiene and 23% styrene) in styrene. The wax was added to the solution (4 parts wax per parts solution) and the mixture was polymerized by heating the solution to 95 C. for, 10 hours with stirring fol- The resin.

. impact. The components of the blend nrayfgener-ally vary from about 37 /2 to about. 87 /2 by Weight of paraffin Wax with the remainder beinga hydrocarbon oil or a soft -wax..

. In order to better illustrate the invention, 'the following examples are. given: i

' Exz zmple I A high impact molding compositionwas. prepared by forming a solution of 5% by weight-.of-S-1006 rubberin styrene. The 8-1006 is a hot rubber containing 77% butadieneyrand 23% styrene. fTo 96 parts by weight of this was added 1 part of mineral'oil A and 3 parts of paraffiin wax C. The mixtureis then subjected tothe conditions set forth to form a polymer. 1

10 hours -at.95, C. with stirring 4-hoursat C.' without stirring 4 hours at C.. Withoutstirring 3 hours, at C. without stirring 12,.hours at 180 C. without stirring The resulting polymer wasmi-lled on a tworoll mill with differential roll. speeds at, C. for five minutes and molded into test bars. 'Phepr-operties are shown in Table II below. Another run. was made according to procedure given above except'that the lubrioantconsisted of 2 parts lowed'by' the following periods of heating Without further 55 ;of mineraloil A-and 2 partsof paraffinwax C.- The reagitation: v V sults of this runare also given in Table II below. Simj 4 hours at 110 C. ilarly,'runs were made using 4 parts of parafiin wax C and 4 hours at 125 C. 4 parts'of mineralwoilAtor the sakeof comparison, and 3 hours at 145 C. the results of. these two; runs are also given in Table II 12 hours at C. 0 below. I

' TABLE .11

r Hardness Heat j a Impact Lubricant Tensile, Yield, Elongg, Roek- Dish, Flow, Izod 1 -p.s.l. p.s.i. percent Wel1, M C. 7 Notched, it. lbs/in.

Parafirn Wax o 3,060 2, s00 21 30 08 123 o. as 3 parts paraffin Wax G-1 part mineral oil A 2,700 2,800 28 as 67.5 125 1.09, 2 parts parafiiu wax 0-2 parts mineral 1 oilA 2, 500 2,700 '29 as so" .96 4 parts mineral oil A 2, 300 2, 100 "31 a I 34 71 p 129 93 -Thepolyrrier was then given-5 minutes of milling at 170 C. ona 6 inch, 2-inol1 rubber mill with difierential roll 75 oilgives an excellent balance of, properties while either Fromthe table, itis seen that-the. mixture offwax and one alone is unsatisfactory. The results are particularly good when the proportions are of the order of 3 parts by weight of parafiin wax to 1 part by weight of mineral oil although good results are obtained When the proportions lie in the range from about 1.5 to 3.5 parts paraffin wax to a suflicient amount of oil to bring the sum to 4 parts.

Example II The procedure of Example I was repeated except that mineral oil A was replaced by a difierent oil in one set of 6 thenic oil or wax is blended with a paraflin wax which is high in normal alkanes.

We claim as our invention:

1. A high impact polystyrene molding composition comprising from about 85 to about 98 parts by weight of polymerized styrene, from about 2 to about 15 parts by weight of a rubber polymer, and from about 1 to about 6 parts by weight of a lubricant, said lubricant comprising from 0.5 to about 2.5 parts by weight of a hydrocarbon oil (and from about 1.5 to about 3.5 parts by Weight of a 111115 and y a $0511 will! in anothel The and soft 10 parafiin wax which consists substantially only of alkanes wax are obtained from the medium lubricating O11 fraction d hth d hi h has a eltin point bet n described under the procedure for panaflin wax B above. 40 d 70 C, This medium lubricating Oil is the fraction distilling 3 1; 2 The molding composition of claim 1, in which said 250 F. at reduced pressures. A high y-iscosity index 0 l 15 rubber polymer is a butadiene-styrene copolymer and said taken fi'om this fraction 18 used in thls example and 1S wax contains above about 60% normal alkanes. designated as HVI Split oil. The soft wax is obtained when the crude wax has been treated to remove praraflin Refe en e Cited by the Examiner wax B. The hydrocarbon oil will contain considerable branching .and naphthenic groups and so will the wax. 20 UNITED STATES PATENTS An analysis of a typical soft wax is 17.6% n-paraffin, ,38 98 8/45 Morley 260285 39.4% isoparatfins, 29.0% mononaphthenes, 3.7% di- 2,808,386 10/57 DAlelio 25028.5 naphthenes and 4.1% aromlatics of which 1.4% are naph- 2,844,562 7/58 Ingram 26045.5 thenes. Thus the wax might be characterized as a highly 2,967,817 1/ 61 Marple et al 260-28.5 naphthenic wax. The results obtained with these lubricants are shown in Table III below: MORRIS LIEBMAN, Primary Examiner.

TABLE III Hatd- Heat Rossi- Yield E1ong., ness Dist. Peakes Impact Lubricant strength, percent Rock- Temp., Flow Izod p.s.l. well, 0. Temp,

3 parts paratfin wax G- 1 part soft wax 2, 500 26. 5 33 67 126 1. 04 3 parts paratfin wax C 1 part HVI split oil. 2, 800 27 27 126 1. 1 2 parts paraffin wax O 2 parts HVI split oil- 2, 900 29 126 4 parts HVI split oil 2, 33. 5 128 From the above data, it is seen that improved properties are also obtained when a highly branched and high naph- ALLAN M. BOETI'CHER, MILTON STERMAN,

ALEXANDER H. BRODMERKEL, Examiners. 

1. A HIGH IMPACT POLYSTYRENE MOLDING COMPOSITION COMPRISING FROM ABOUT 85 TO ABOUT 98 PARTS BY WEIGHT OF POLYMERIZED STYRENE, FROM ABOUT 2 TO ABOUT 15 PARTS BY WEIGHT OF A RUBBER POLYMER, AND FROM ABOUT 1 TO ABOUT 6 PARTS BY WEIGHT OF A LUBRICANT, SAID LUBRICANT COMPRISING FROM 0.5 TO ABOUT 2.5 PARTS BY WEIGHT OF A HYDROCARBON OIL AND FROM ABOUT 1.5 TO ABOUT 3.5 PARTS BY WEIGHT OF A PARAFFIN WAX WHICH CONSISTS SUBSTANTIALLY ONL, OF ALKANES AND NAPHTHENES, AND WHICH HAS A MELTING POINT BETWEEN 40* AND 70*C. 